In general, semiconductor materials may be processed in semiconductor technology on or in a substrate (also referred to as a wafer or a carrier), e.g. to fabricate integrated circuits (also referred to as chips). During processing the semiconductor material, certain process steps may be applied, such as thinning the substrate, doping a semiconductor material, or forming one or more layers over the substrate.
For doping the semiconductor material, a dopant may be implanted into the semiconductor material. The semiconductor material may be further processed to fully activate the dopant. Dopant activation may provide obtaining the desired electronic contribution from the dopant in the semiconductor material. For activating the dopant, thermal energy may be transferred to the semiconductor material following the dopant implantation. Conventionally, thermal annealing by a furnace or rapid thermal processing is used, providing a thermal equilibrium or a rapid process, with a high peak temperature for less than one second to minimize chemical diffusion of the dopant. For transferring thermal energy to the semiconductor material, laser light may be used, also referred to as Laser-Thermal Annealing (LTA).
Conventionally, a wavelength of the laser light is adapted according to the semiconductor material to provide a maximum transfer of energy to the semiconductor material. In other words, a high transfer efficiency may be provided, which reduces the energy needed for LTA. Alternatively, the wavelength of the laser light is adapted according to the desired absorption length. A short wavelength may result in a concentration of energy in the surface portion.
One the one hand, due to the high absorption, also the penetration depth of the laser light may be limited depending on the wavelength of the laser light. The total energy of the laser light may be limited according to the thermal limits the semiconductor material can withstand. Therefore, the process itself may limit a depth of the semiconductor material in which the dopant is activated.
On the other hand, even if the wavelength of the laser light is adjusted according to a maximum transfer of energy, still a large portion of the laser light is inherently reflected by the semiconductor material and cannot be used for transferring energy to the semiconductor material anymore. For example, the semiconductor material reflects conventionally about 60% of the laser light. Therefore, the total energy needed to obtain a desired amount of thermal energy transferred to the semiconductor material is much higher than the thermal energy. In other words, the power consumption of the laser light source and the corresponding investment costs to provide process equipment having the required power capability (e.g. sufficient optics, multiple pulse lasers, and multiple wavelength lasers) are conventionally high.
Conventionally, an antireflective coating is formed over the semiconductor material to reduce the amount of reflected light. However, the antireflective coating may affect the result of the thermal treatment due to mechanical stress incorporated in the antireflective coating. Conventional antireflective coatings are based on an interplay of constructive interference and destructive interference provided by a complex layer architecture, and therefore may need high effort to be prepared. Further, inherent stress may be built into the antireflective coating due to the preparation, which may relax when the underlying portion of the semiconductor material is melted. The topographical image of the relaxed antireflective coating may be in incorporated into the solidifying portion of the semiconductor material. A compressively stressed coating tends to crack and to spall if the support by the mechanically rigid underlying semiconductor material is lost due to its melting. Further, the coating may intermix with the melted semiconductor material and contaminate the semiconductor material. This may lead to processing faults or limit the processing range, e.g. the thermal treatment.